1. Field of the Invention
The present invention relates to adjustment mechanisms for use in medical appliances.
2. Summary of the Prior Art
It is known to use electrically operated devices for a variety of purposes in medical applications. In these devices, it is desirable to be able to easily adjust, and if necessary, instantly zero, an output parameter such as current amplitude. A system for delivering heated humidified gases to a patient is disclosed in U.S. Pat. No. 5,558,084. In systems of this type, a switch, button, rotating knob or similar is included, which is used to adjust the level of heating or flow. The inventors have recognised a need for control systems on these devices which can be easily adjusted, and where the output current, or another output parameter, can be instantly zeroed if required. An operator of any of these devices would find it useful to be able to easily and instantly adjust the output via the adjustment switches, buttons or knobs on these devices, so that power or current, for example to the heater, the fan, or similar can be instantly zeroed. In particular, it would be desirable to instantly and easily zero the magnitude of the current amplitude, with no adjustment lag. One reason for the desirability of including a switch of this type is to avoid user discomfort caused by excessive flow pressure or excessively hot gases, or for example in order to avoid patient discomfort or tissue damage.
Another example of a device that may benefit from an instant zero is a radiant heater, such as the one described in U.S. Pat. No. 6,719,780. If a medical professional requires the power to be instantaneously shut off, or the current to be instantly zeroed, it would be useful for them to have access to a control device or switch that allows this.
Other medical devices that would benefit from including an instant zero include positive pressure breathing machines, and nerve stimulators. Outlined below are typical nerve stimulation operations and associated hardware, exemplifying why devices that include an instant zero are required.
In nerve stimulation and location, individual nerves or nerve bundles in a body are stimulated by application of an externally applied low-level electric current. This has several advantages in modern medical practice. For example, if the location of nerve bundles or nerve nexuses in a body is accurately known, these can be avoided during invasive surgery, decreasing the chances of damage to the nerves of a patient. A further advantage is in general or local anaesthesia, where nerve stimulation techniques can be used to locate the best site for the injection of local anaesthetic, to judge an appropriate amount of anaesthetic, or to judge the level of anaesthesia of a patient.
Nerve stimulation is carried out by applying an electric current to a location on the body of a patient, usually close to a nerve nexus. The reaction of the body part (twitch response) is observed as the current amplitude, current pulse frequency, and (in some operations) the location of a current carrying electrode are altered. In this manner, nerve locations or an anaesthesia level, or both, can be judged.
There are several specialist nerve stimulator devices currently on the market, for use in operating rooms or similar, which can deliver low-level electric current for nerve stimulation or detection. Normally, these devices are battery-powered, and are sized so as to fit the palm of a users hand. A typical device is the ‘Innervator NS272’, as manufactured by the applicant and shown in FIG. 1. Probes or electrodes suitable for delivering a low-level current to a user are connected to the nerve stimulator via connected leads. An example of these combination leads and electrodes is shown in FIG. 2a. In some applications, such as nerve location, a user may prefer to use a combination drug administration needle and electrode. An example of this type of combination is described in U.S. Pat. No. 6,706,016. The electrode/needle is used to locate a nerve or nerve nexus close to an area where local anaesthetic is required, with anesthetic delivered directly to the area via the needle.
Alternatively, a user may prefer to use a double-headed shrouded diagnostic probe, similar to the one manufactured by the applicant, and shown in FIG. 2b. This connects directly to the output of the nerve stimulator, and is brought into contact with the patient where required.
In most nerve stimulators, the current output and other useful information is displayed to a user on a display screen. A user holds the nerve stimulator in one hand, and observes output readings such as current amplitude on the display, while using their free hand to locate an electrode in or on a user.
It is common practice to detachably mount the nerve stimulator on a bracket, pole or similar, so that a user has both hands free to manipulate electrodes or other equipment, while still easily observing output readings.
Usually, nerve stimulators are operated in one of two main modes, a first mode where the device is used for nerve location, and a second mode where the device is used for nerve stimulation.
The nerve location mode is used when nerve locations need to be accurately mapped, for example so that these locations can be avoided when carrying out invasive surgery around that area. Nerve location is also used in local anaesthesia, when it is desired to administer the anaesthetic drug as close to a nerve as possible, without the drug administration needle touching the nerve.
The general process that is usually followed for nerve location can be outlined as follows:
Nerve locations in the human body are known approximately, with the exact locations varying from individual to individual. In order to accurately locate nerves on a patient, a first sensor/electrode is attached close to a known nerve location, by taping the sensor to their skin, or similar. The initial location of this first electrode is normally judged ‘by eye’. A second electrode (or electrode/needle combination) is also connected to the nerve stimulator. An operator touches the second electrode to the skin of the patient, close to the first sensor. If the second electrode is an electrode/needle combination, the tip of the needle is usually inserted into the muscle, close to a nerve or nerve nexus location. The current from the nerve stimulator fires nearby nerves and causes the associated muscles to contract, or twitch. The nerve stimulator current can be pulsed, e.g. at a frequency of 1 Hz, in order to help an operator observe the ‘twitch response’. Depending on observations of the ‘twitch response’, an operator can judge the nerve location and administer drugs appropriately.
It is usual practice to commence a nerve location search with a current amplitude of between 0.6 mA and 2 mA. The exact value will depend on the preference of the individual practitioner. However, the starting current amplitude is usually kept low, with the operator or user judging the initial twitch response and increasing the current amplitude if necessary. Starting the operation at a low current level helps avoid patient discomfort, and reduces the possibility of damage to a patients nerves. If no twitch response is observed at a low current output, the current amplitude is increased until a response is observed. The location of the nerve relative to the electrode can be judged, and the electrode or needle moved closer to the nerve, with the current amplitude and pulse frequency adjusted until the nerve location mapping is completed. It is considered good practice to reduce the current amplitude as the electrode is moved closer to the nerve, in order to avoid discomfort or damage. The pulse frequency can be increased to compensate for the reduced current amplitude, so that the twitch response remains observable. If the current level is reduced to approximately 0.2 mA, and muscle twitches are still observable, then the needle is known to be approximately 2 mm from the nerve. If using a needle/electrode combination, an anaesthesia drug can be directly administered at this location.
Nerve stimulation methodology is normally used when a patient is or will be under general anaesthesia (fully paralysed). In nerve stimulation, the aim is to find the supramaximal current. This is the current level that causes all nerve fibres in a bundle to fire at the same time, and is usually between 4 OmA and 5 OmA for most humans. If the supramaximal current is known, appropriate doses of anaesthetic can be administered. Also, post-anaesthesia administration, if a current is applied at the supramaximal level, and no response is observed, this is a reliable indication that the anaesthesia is working correctly.
There are two main methods which are normally used for finding the supramaximal current value for an individual. These are outlined below.
In the first method (pre-anaesthesia), current is applied to the body in a similar manner to that outlined above for nerve location, starting at a low initial current amplitude value (usually the lowest possible value the nerve stimulation unit is capable of). The current amplitude is gradually increased to the point where a twitch response is just observable. The supramaximal current amplitude for the individual is three times this level.
In the second method (post-anaesthesia), the patient is anaesthetised before any nerve stimulation is carried out. Nerve stimulation is carried out, until the maximum twitch response is observed (that is, the point at which increasing the current amplitude no longer increases the size of the twitch response). The supramaximal current value is 120-130% of the amplitude of this current level.
Several devices exist that can be used for nerve stimulation and location. Devices also exist which can be used to measure the twitch response in a more accurate fashion than can be achieved with simple observation ‘by eye’.
The applicants ‘Innervator™’ range can be used to carry out the operations described above. An example, the ‘Innervator NS272’, is shown in FIG. 1. The current amplitude and other parameters are controlled by means of standard buttons on the upper surface. Standard in this context should be taken as meaning that the buttons are inactive until depressed. The buttons have one depressed position, and when depressed, will activate or carry out one pre-set or hardwired function.
The controls of the NS232 model also include a button pair, one of the pair used to increase current amplitude in incremental steps when depressed, and the other used to decrease current amplitude in incremental steps.
One problem that can occur when carrying out nerve stimulation in the manners described above is patient discomfort or, in some cases, nerve damage. As nerves are extremely sensitive to electric current, minor changes in the position of a current-carrying electrode or needle close to a nerve can cause discomfort or damage. This can occur even when an operator is paying due care and attention, and carrying out location and stimulation methodology in accordance with best practice. With some existing nerve stimulators it is also possible, through human error or carelessness, to touch an electrode to the body with the current amplitude set to a high or maximum value, and the unit turned on. If the electrode is initially applied with a high current output, close to a nerve, this can cause discomfort or damage. In some situations it can be difficult to immediately remove an electrode from contact, for example if a needle/electrode combination is being used, and care would need to be taken to remove the needle. It may also be the case that removal of an electrode from contact with the body at that moment is undesirable, for example if an electrode/needle is suitably located for administration of anaesthesia. It is therefore useful for an operator to be able to rapidly or instantaneously decrease the current output to zero.
Life-tech, Inc. manufacture a nerve stimulator and locator, which offers a similar functionality to the ‘Innervator™’ range. The Life-tech. Inc. ‘Tracer® III’, shown in FIG. 4, has a central knob, which a user rotates clockwise or anticlockwise to adjust the amplitude of the current. In order to ascertain with any precision what the current amplitude value is (i.e. the exact position of the knob), the unit must first be switched on.
Another product which uses a central knob to control the amplitude of the current is the ‘Stimuplex® HNS11’ manufactured by B Braun, shown in FIG. 3a, and in use in FIG. 3b. The central control knob of the ‘Stimuplex® HNS11’ acts as an on/off switch. Rotating the knob to the furthest anticlockwise position turns the unit off.
Nerve stimulators that use central knobs offer a responsive and easily adjustable current output. However, if the central knob is used as the main current control mechanism, it needs to be rotated through a range of movement (i.e. from the use position, to zero), in order to zero the current output.
The ‘Tracer® III’ offers the additional functionality of a pause button, which is said to cut the current flow to an attached electrode. This pause button is located remotely from the central knob. An operator using both hands to adjust the unit can keep one on the control knob, and one on the pause button, making adjustments to the current amplitude as required. If necessary, the operator can depress the pause button and zero the current output. An operator using both hands in this manner may find it difficult to make adjustments to the position of an electrode. If an operator is using one hand to adjust the electrode position, and the other to alter the current, they will need to move their hand from the control knob in order to reach the pause button. Similarly, if an operator is holding the unit in one hand, (or if it is supported on a stand), with one hand being used to make adjustments to the current amplitude, and the other being used to position an electrode, an operator will need to move their hand from the control knob, over to the pause button in order to cut the current output.
Several other control mechanisms for nerve stimulator devices are available which can be used to minimise user discomfort, and increase ease of use for an operator. U.S. Pat. No. 6,706,016 describes an electrode and anaesthesia needle combination, where the current control switch is located on the electrode. The electrode/needle combination is connected to a remotely located nerve stimulator. The switch allows an operator to alter the current, using the same hand they are using to change the location of the electrode/needle.
In U.S. Pat. No. 5,830,151, the current amplitude from the nerve stimulator is controlled by means of a connected and remotely located foot pedal, which is depressed by a user in order to increase the current. When the operator removes their foot from the pedal, the current remains at a constant amplitude.
One other output that a user may wish to easily adjust or trigger is current pulses at pre-programmed amplitudes and pulse frequencies. A user may also wish to quickly and easily change the current amplitude or pulse frequency if these need adjusting after a user has commenced use. It can be seen that there is an identified need for devices that enable a user to make these adjustments easily and via conveniently located controls.
The inventors have recognised a need for medical devices including nerve stimulators where the current amplitude and other outputs are easily adjustable. An operator would therefore find it useful to have access to a medical device such as a nerve stimulator where all the controls are easily accessible and easily adjusted, for example by using one hand or one digit (e.g. the thumb of the hand holding the nerve stimulator), and where the number of sub-operations or manipulations to the controls required when in use is kept to a minimum. The inventors have particularly determined that it would be desirable to be able to instantly and easily drop the magnitude of the current amplitude from a nerve stimulator to zero with no adjustment lag, in order to avoid patient discomfort or nerve damage